The invention relates to a dust filter for a ducted air delivery system and relates particularly but not exclusively to dust filters suitable for fitting into the plenum of air ducts.
Air conditioning and air heating systems for homes and offices commonly include a number of ducts for delivery of the heated or cooled air, the ducts terminating in outlets spaced at various locations around the home or office with the spacing being chosen to give an even distribution of heating and/or cooling over the area concerned. Typically, the outlet of such ducts is in the form of a plenum which is covered by an exhaust air register.
Over time, dust can collect in the ducting system or it can be recirculated through the ducting system by the heating or cooling unit. Such dust which includes particulates such as moulds, pollens and the like will cause a build up of dust in the area immediately surrounding the registers. Furthermore, the airborne dust circulated by the system can affect the health of susceptible individuals, particularly those affected by respiratory problems such as asthma.
To overcome this difficulty, various types of filter constructions have been proposed. However they all suffer from various disadvantages. For example, they may be relatively complex, making them expensive to manufacture, difficult to install and difficult to remove for cleaning.
Thus there is a need for a dust filter construction which can be readily installed and is of such simple construction that it can be manufactured at reasonable cost.
The invention provides a dust filter for a ducted air delivery system comprising,
a frame defining an open mouth, the frame having a body portion formed of rubbery thermoplastics material reinforced with one or more stiffening elements,
a filter material extending from the sides of the frame to cover the open mouth, and
an integral lip of flexible resilient material extending outwardly from the body portion, the integral lip being less than half the thickness of the body portion over most of its extent,
wherein the lip of flexible resilient material is shaped so that it may make a friction fit within the outlet of a duct to hold the dust filter therein.
Typically, the dust filter is shaped so that it fits snugly in the plenum forming part of the outlet. The plenum forms a friction fit therewith and may be covered by a conventional exhaust register.
Suitably, the dust filter may include means to facilitate manual gripping of the filter so that it may be conveniently removed from the plenum after it has had a certain amount of use. Such gripping means may comprise one or more handles provided on the frame. Such one or more handles may be in the form of an integrally formed post extending upwardly from the frame. Alternatively the gripping means may comprise a plurality of integral tabs extending from the lip.
In order to assist with the friction fit characteristics of the filter, it is preferred that the lip extends laterally from the frame.
The lip may take any suitable shape; for example it may be straight, curved or V-shape. It may be dimensioned so that pushing the dust filter downwards into a plenum has the effect of bending the lip to push the edges of the lip upwards. In this way, the edges of the lip will press against the sides of the plenum chamber and will resist upwards pressure on the dust filter, by air flowing upwardly therethrough, to retain the filter in the plenum.
Suitably, the frame of the dust filter includes a body portion which is moulded from a rubbery thermoplastics material such as natural rubber, polyurethane or silicone rubber. However silicone rubber is particularly preferred.
In order to strengthen the frame which comprises rubbery material, the one or more stiffening elements may be retained in a recess or recesses formed in the body portion of the frame.
In a particularly preferred aspect of the invention, a stiffening element formed in one piece which extends around the body of the frame may be provided. With such an arrangement, it is preferred that the thermoplastic material comprising the body portion be moulded directly onto the frame thereby securing the stiffening element within the frame.
The stiffening element itself may be formed of any material which can lend stiffness to the frame. For example the stiffening element may comprise a square or rectangular member made of metal or hard plastic. The dimensions of the member may be slightly smaller than the dimensions of a rectangular or square plenum in which the dust filter is to be retained.
In one form of the invention, the filter material and the thermoplastic material comprising the frame may be heat welded together. Alternatively, the filter material may be friction fitted into the recess for holding the one or more stiffening elements in association with such stiffening elements.
In another form of the invention, the filter material may be bonded to an integrally formed internal ledge extending from a body portion of the frame around the open mouth.
The dust filter itself may comprise a plurality of fibres. It may comprise a batt of non-woven fibres. Examples of suitable fibres include polyester, fibreglass, wool, cotton, arylamides or arylimides.
An indicator may be provided on the dust filter. The indicator may be adapted to indicate that the dust filter needs replacement or cleaning. It may be a time based indicator ie. it automatically indicates when a period has expired after manufacture of the dust filter. For this purpose, it may be a form of chemically active printing which changes color or indicates in some other way that the filter has reached an age at which it should be replaced. It may be invisible when the filter is first manufactured and may become visible under time with a message to indicate that the filter needs replacement or cleaning. For example the word xe2x80x9cexpiredxe2x80x9d or the words xe2x80x9creplace mexe2x80x9d may become visible over time.
Alternatively, the indicator may include a physical or chemical treatment which is based upon the amount of use the filter has received. For example, the bat of fibres comprising the filter element may include regions where the density of fibres is deliberately increased eg. they may be compressed. As the regions of greater density will have a reduced air flow therethrough, they will tend to pick up less dust. Over time, the dust pick up on the remainder of the filter will be clearly visible compared with the regions of higher density. Thus if the regions of higher density are formed as words, over time, the dust collected by the filter will make these words more visible hence giving an indication to the user that the filter needs to be cleaned or replaced.